CROSS-REFERENCE TO RELATED APPLICATION
The present application is related to U.S. patent application Ser. No. 09/019,767, filed on Feb. 6, 1998, now abandoned in favor of a co-pending continuation application Ser. No. 09/274,561, filed on Mar. 23, 1999. In these related applications there are described a number of improved protection systems based on those disclosed in Ser. Nos. 08/869,905, 08/682,067 and 08/682,172. The entire disclosure of U.S. patent applications Ser. Nos. 09/019,767 and 09/274,561 is incorporated herein by reference for all purposes. The present invention provides further improvements in the systems disclosed in Ser. Nos. 08/868,905, 08/682,172 and in Ser. Nos. 09/019,767 and 09/274,561 having the same filing date as the parent of this application.
1. Field of the Invention
This invention relates to electrical systems which contain positive temperature coefficient (PTC) circuit protection devices, particularly such systems in automobiles and other wheeled vehicles.
2. Introduction to the Invention
PTC devices are well known. Particularly useful devices contain PTC elements composed of a PTC conductive polymer, i.e. a composition comprising an organic polymer and, dispersed or otherwise distributed therein, a particulate conductive filler, e.g. carbon black, or a metal or a conductive metal compound. Such devices are referred to herein as polymer PTC, or PPTC, devices. Other PTC materials are also known, e.g. doped ceramics, but are not as generally useful as PTC conductive polymer, in particular because they have higher resistivities. PTC devices can be used in a number of different ways, and are particularly useful in circuit protection applications, in which they function as remotely resettable fuses to protect electrical components from excessive currents and/or temperatures. Components which can be protected in this way include motors, batteries, loudspeakers and wiring harnesses in automobiles. The use of PPTC devices in this way has grown rapidly over recent years, and continues to increase. Reference may be made for example to U.S. Pat. Nos. 4,237,441, 4,238,812, 4,315,237, 4,317,027, 4,426,633, 4,545,926, 4,689,475, 4,724,417, 4,774,024, 4,780,598, 4,800,253, 4,845,838, 4,857,880, 4,859,836, 4,907,340, 4,924,074, 4,935,156, 4,967,176, 5,049,850, 5,089,801, 5,378,407, 5,451,919, 5,451,921, and 5,645,746, and to copending commonly assigned U.S. application Ser. No. 08/900,787 (Graves et al., filed Jul. 25, 1997), now U.S. Pat. No. 5,852,397 the disclosures of which are incorporated herein by reference for all purposes.
More recently, it has been proposed to combine PTC devices with other electrical components to provide circuit protection systems which respond to faults in ways which make use of the characteristics of both the PTC device and the electrical component. Reference may be made for example to U.S. Pat. Nos. 5,666,254 and 5,689,395, and to copending commonly assigned U.S. application Ser. Nos. 08/564,465 (Duffy et al., filed Nov. 29, 1995), now U.S. Pat. No. 5,864,458, Ser. No. 08/563,321 (Duffy et al., filed Nov. 28, 1995), now Pat. No. 5,745,322 Ser. No. 08/584,861 (Duffy et al., filed Jan. 5, 1996), abandoned in favor of continuation application Ser. No. 09/145,799, filed on Sep. 2, 1998, which has been abandoned in favor of continuation application Ser. No. 09/311,785 filed on May 14, 1999 Ser. No. 08/658,782 (Duffy et al., filed Jun. 5, 1996) now abandoned 08/682,067 (Myong et al., filed Jul. 16, 1996) abandoned in favor of continuation application Ser. No. 09/156,933, filed Sep. 18, 1998 and 08/682,172 (Myong, filed July 16, 1996) and 08/868,905 (Myong, filed Jun. 4, 1997), abandoned in favor of continuation application Ser. No. 09/248,166, filed on Feb. 9, 1999 the disclosures of which are incorporated herein by reference for all purposes.
Ser. Nos. 08/682,067 and 08/682,172 describe protection systems which comprise a sensor element (typically a resistor) and a circuit interruption element (typically a relay) in series with the load, and a control element (typically a PTC device in parallel with the sensor element) which links the sensor element and the circuit interruption element so that an overcurrent is detected by the sensor element, and causes a change in the control element, which in turn causes a change in (typically opens) the circuit interruption element. Depending on the arrangement of these and other components, the system can (a) latch in an open state, either with or without a trickle current to keep the PTC device in a tripped condition, or (b) reclose if the overcurrent has gone away or cycle between open and closed positions if the overcurrent remains. Ser. No. 08/868,905 describes particularly useful devices for use in the protection systems of Ser. Nos. 08/682,067 and 08/682,172.